Thousands of nesting birds have abandoned their eggs at Seahorse Key off Florida's Gulf Coast leaving biologists baffled. Little blue herons, roseate spoonbills, snowy egrets, pelicans and other chattering birds were gone, appearing to have left the island all at once in May. Nests sat empty in trees; eggs broken and scattered on the muddy ground, biolgists noted, according to dbtechno.com.

"It's a dead zone now. This is where the largest bird colony on the Gulf Coast of Florida used to be," Vic Doig, a U.S. Fish and Wildlife Service biologist said about the sudden disappearance, according to dbtechno.com.

Doig said some of the Seahorse birds seem to have moved to a nearby island, but they're just a fraction of the tens of thousands of birds that would normally be nesting on the key right now.

To find answers, service biologists have been acting on the few clues:

First, they tested left-behind bird carcasses for disease or contaminants. Those tests came back negative.

Next, they researched possible new predators. Did raccoons swim over from another island? Perhaps some great horned owls flew out at night and started feasting?

Traps caught a few raccoons, which is common, but not enough to have created a wholesale abandonment. There were no telltale signs of owls.

Lastly, while admittedly a longshot, Doig said, they checked if an increase in night flights over the area by surveillance planes and helicopters used to combat drug runners proved too disruptive for the birds causing them to leave.

The abandonment concerns biologists because it could have a ripple effect. Many bird species here return year after year to the same nesting sites. The disruption provokes anxiety that this important island refuge could somehow be lost, according to Fox News.

Biologists also don't know how the disappearance will affect the island's other animals, some of which rely on the birds to survive. For example, cottonmouth snakes eat bird predators like rodents, and in turn the birds drop lots of fish and other nutrients from the trees to feed the snakes, according to the Tampa Bay Times.

As a result, tour operators that once spent hours taking naturalists and bird watchers to the island are making other plans.

Mike O'Dell runs tours out of the little marina in nearby Cedar Key. He said on a Tuesday in May he led a group out to view thousands of birds crowding the shores of the key. On Wednesday, there was nothing, according to U.S. News.

"It's just that drastic. There were none. It's like a different world," he said.